Commercial, gas-fired tunnel ovens equipped with conveyors produce, among other things, pizzas, cookies, bread, cakes and donuts. Each oven routinely processes a large volume of food products and, as a result, becomes rather dirty. Bits of the food products themselves, burned food products, and soot from the burners are typical sources of contamination that accumulate during use.
Gas-fired tunnel ovens traditionally have been cleaned manually with detergent and acid solutions. The oven must be taken apart for cleaning by these methods. In addition to the oven walls, roof, and floor, the conveyor used with the tunnel oven must be cleaned, as well as any jet-impingement convection fingers, convection blowers, and fired burners. Cleaning by the traditional methods is tedious and expensive.
In theory, a gas-fired, commercially-sized tunnel oven might be cleaned by installing electrical heaters at critical points to raise the internal temperature to a range that reduces virtually all contamination to ash. In practice, cleaning a gas-fired tunnel oven by raising the temperature with electrical heaters requires an estimated 50-100 amperes of electricity for each oven. Commercial bakers do not normally have access to this much electrical current, and the cost of installing high current electrical service is a significant financial barrier for most bakers.
Accordingly, there is a need for a self-cleaning, gas-fired tunnel oven suitable for use with a conveyor that can be cleaned without need of disassembly, manual cleaning, or detergents. Commercial bakers would welcome a self-cleaning, gas-fired tunnel oven.
A self-cleaning, gas-fired tunnel oven that cleans by pyrolysis is provided. The oven is used with a conveyor for food products, which may be collapsed and placed inside the oven for pyrolitic cleaning. The oven includes a control system that regulates the oven temperature and duration of the self-cleaning operation and deters people from opening the oven during the self-cleaning operation.
The control system also modulates combustion air and heating gas to one or more burners within the oven. A modulating control system regulates the flow of air or heating gas to the burner or burners. The ratio of airflow to heating gas flow is controlled directly so that the ratio of air to fuel gas flowing to the burner is approximately the same over a range of heating loads. The control system that proportionally coordinates the flow of air and fuel may be, for example, a mechanical linkage between the valves or one or more electric or pneumatic controllers that send positioning signals to the valves. With modulating control of combustion air and heating gas, the oven operates cleanly and efficiently over a wide range of heating loads.
The oven may be equipped with a plurality of convection blowers, each of the convection blowers being subject to individual speed control. The speed of one or more of the convection blowers is varied during start-up operation to optimize fuel consumption, during cooking operation to optimize the quality of food products cooked in the oven, and during the self-cleaning operation to control the rate of contaminant incineration, among other reasons.
The oven includes a floating cooking chamber, which can withstand pyrolitic cleaning temperatures and repeated pyrolitic cleaning cycles without warping, cracking or developing metal fatigue. Various components of the floating cooking chamber are joined in a sliding fit that permits the floating cooking chamber to expand and contract in response to temperature changes without applying excessive mechanical stress to the components.
The oven also includes a vacuum exhaust system for exhausting pyrolysis products. In one version, the convection blowers are situated to deliver convection air to the oven and, also, maintain the oven under a negative pressure with respect to the kitchen. In another version, an inducer blower extracts the exhaust air from the oven and delivers it to a disposal system. The negative pressure prevents combustion products produced during the self-cleaning process from escaping to the kitchen.
The oven is equipped with an active cooling system in which air from the kitchen is passed through ducts that cool the exterior surfaces of the oven. The oven includes heat-slingers to protect the shafts of the convection blowers from overheating. Additionally, the oven includes self-cleaning fingers for a jet-impingement convection system that also clean the conveyor.